1. Field of the Invention
The present invention relates to new liquid coating compositions useful for the production of improved fluorine-doped tin oxide layers preferably made by chemical vapor deposition processes. Such coatings find use in insulating glass for houses, in conductive glass for plasma TV screens, etc. The obtained coatings, which also make up a part of the invention, have high conductivity, high visible light transmittance, and low haze.
2. Description of the Related Art
Fluorine-doped tin oxide coatings are known to be conductive layers. Several chemical compositions and methods of production have been described in the literature regarding the manufacture such tin oxide coatings:
Japanese patent 75-61,415 utilizes a spray of chemicals present in a large amount of solvent, which produces significant technical and environmental problems, and which is not usable in a C.V.D. (Chemical Vapor Deposition) process.
European patent EP-A-0 112 780 describes a method using alkyl chloro tin and a gaseous alkyl chloro fluorocarbon which provides severe problems with regard to toxic waste by-products as well as difficulties in handling and controlling the gas.
U.S. Pat. No. 4,265,974 describes a method using tetramethyl tin, which is very toxic and explosive in air.
U.S. Pat. No. 4,293,594 describes a method using dimethyl tin difluoride, which is a powder too difficult to be vaporized.
U.S. Pat. No. 4,601,917 describes a method using a chloro tin compound doped with an organic fluorine compound selected from trifluoroacetic acid, trifluoroacetic anhydride, ethyl trifluoroacetoacetate, trifluoroethanol, ethyltrifluoroacetate and pentafluoropropionic acid. The presence of an oxygenated functional group in the molecule of the fluorine dopant promotes the formation of oxidized build-up before pyrolysis on the glass.
U.S. Pat. No. 4,857,095 describes a method using dibutoxydibutyl tin with trifluoroacetic acid. The presence of oxygen bonded to tin prevents the good formation of the tin oxide layer and gives numerous white deposits in the fume evacuation circuit.
Japanese patent JP-A-62,70247 describes a method using dibutyl tin (or dimethyl tin) di-trifluoroacetate or butyl tin tri-trifluoroacetate with trichlorobutyl tin or tetrachloro tin. The presence of chlorinated solvent in all solutions renders the composition dangerous and toxic. Moreover, it promotes the appearance of corrosive green deposits in the fume evacuation circuit.
French patent 93-05245 describes a method using a chlorinated organo tin compound doped with organo tin monofluoroalkanoate and a tetraorgano tin. The use of such a heavy fluorine dopant promotes the appearance of black deposits in the vapor circuit due to the high temperature of vaporization needed.
From the above description of the prior art, the need for a new composition useful in a CVD process giving improved conditions of vaporization, avoiding environmentally toxic waste and giving high conductivity, high visible light transmittance coatings on, for example, glass, is clear.
In accordance with the invention, there is provided herein a new liquid coating composition very well adapted for use in the chemical vapor deposition of a coating on glass substrates which:
provides a very conductive layer, with low haze and high visible light transmittance.
has a low temperature of vaporization which avoids decomposition, keeping the vaporization circuit essentially free of deposit.
does not require and preferably does not contain any dangerous or toxic component.
upon pyrolysis avoids significant production of corrosive dust and environmental pollutants.
The invention composition comprises a chlorinated organotin derivative and a polyfluoroalkyl or halo polyfluoroalkyl dopant.
More specifically, the composition of the invention preferably comprises a mixture prepared by mixing together:
70% to 99% by weight of at least one organo-tin compound, preferably chlorinated organo-tin compound, wherein the tin atom is bonded to at least one carbon atom of a hydrocarbon chain;
1% to 30% by weight of at least one polyfluoroalkyl, halo polyfluoroalkyl, polyfluoroalkenyl or halo polyfluoroalkenyl compound where xe2x80x9chaloxe2x80x9d is halogen other than fluorine (Cl, Br, etc.); and
Optionally up to 29 weight percent of an organic solvent.
The preferred general formula of the organo-tin compound is:
RxSnCl(4-x)xe2x80x83xe2x80x83Compound I 
wherein x is an integer which may vary from 1 to 4 (i.e., 1, 2, 3, 4) and R represents a C1-8 alkyl or alkenyl group having one or more double bonds or a phenyl radical. Preferably, to avoid toxicological problems, R is a butyl radical. To limit the presence of carbon in the layer, x is preferably 1. These compounds are collectively referred to as (chlorinated) organotin compunds. The (chlorinated) organotin compound can also be a mixture of different compounds of the above formula.
The preferred general formula of the polyfluoroalkyl or alkenyl and halo polyfluoroalkyl or alkenyl compound is: CnFmXoHp, where n is at least 4 and preferably less than 25, m is 1-30, preferably 2 or greater, X is halogen other than fluorine, o is 0-30 and p is 0-52. When o is not zero the compound is a halo polyfluoroalkyl compound. When the carbon chain contains one or more double bonds the compounds are alkenyl compounds. These compounds are neutral organic compounds and include linear, branched and cyclic structures. The F, X and H atoms are substituents on the carbon atoms. For simplicity these alkyl and alkenyl compounds are described as (halo) polyfluoroalkyl compounds herein and preferably have boiling points of at least 50xc2x0 C. and more preferably from 50-200xc2x0 C.
One group of preferred species is: 
Where R1, R2 and R3 are each independently hydrogen, halogen, C2-9 alkyl or C2-9 haloalkyl. The compound is a halo polyfluoroalkyl when any one or more of R1, R2 and R3 are or contain halogen other than fluorine.
Preferably, compound II has a boiling point of from 50xc2x0 C. to 200xc2x0 C.
The polyfluoroalkyl or halo polyfluoroalkyl compound can also be a mixture of one or more of these different compounds. Both the polyfluoro and halo polyfluoro compounds may be present.
The composition according to the invention may also optionally comprise up to 29 weight % of an organic solvent such as xylene, methyl isobutyl ketone, dichloroethane, chloroform, CCl4, etc. The solvent should preferably have a boiling point of 40 to 100xc2x0 C. The solvent should be a liquid at STP. The organic solvent of the invention does not include the invention chlorinated organo-tin derivative, polyfluoroalkyl compound or halo polyfluoroalkyl compound.
The invention (chlorinated) organo tin compound, (halo) polyfluoro alkyl compound, and organic solvent are commercially available and/or within the skill of the ordinary artisan to obtain/synthesize.
The preferred way of producing a thin layer of fluorine doped tin oxide on a substrate with the invention composition is chemical vapor deposition. Useful substrates include glass, metal, etc. In this method, the invention liquid composition is vaporized in a continuous boiler at an effective temperature which temperature preferably is below 250xc2x0 C. Then, the vapor can be mixed or carried out with oxygen, air (preferably hot air), and/or steam at a sufficient temperature to keep a complete vapor phase. The mixed vapor is directed on the substrate for pyrolysis. The temperature of the substrate must be higher than 400xc2x0 C., preferably about (xc2x120xc2x0 C.)500xc2x0 C. to 700xc2x0 C.
With this method, a coating of fluorine doped tin oxide can be obtained having the following properties:
Chemical vapor deposition processes are known to those of ordinary skill in the art, and the present invention method utilizing the invention composition is not limited to the example method specifically described.
In a preferred embodiment of the invention compound I is butyl tin trichloride (BuSnCl3). Preferred species of halo polyfluoroalkyl and polyfluoroalkyl include one or more of the following species:
The invention compositions, which are within the skill of the ordinary artisan to make and use, preferably comprise (by weight) from 70% to 99% of the (chlorinated) organo tin compound such as compound I (including 75, 80, 85, 90 and 95%) and from 1% to 30% (including 5%, 10%, 15%, 20% and 25%) of the (halo) polyfluoroalkyl compound such as compound II. Solvent may be present in 29% or less, including 25%, 20%, 15%, 10%, 5%, greater than 0%, and 0%. compositions according to the invention may be prepared by mixing the necessary components together.